This invention relates to the injection of ammonia into a flue for waste gases and, more particularly, to an improved method of injecting the ammonia.
For the purpose of preventing corrosion or generation of an acid smut on the low temperature side of an oil burning boiler, there has been proposed an apparatus for injecting ammonia into a flue for waste gases. As shown in FIG. 1, such an apparatus generally comprises a liquefied ammonia tank a, a liquefied ammonia evaporator g, nozzle pipes c arranged within flue b at the exit of an air heater and provided with equal size nozzles or openings j and with shut-off valves J, for cleaning of the nozzles, orifices d, d, a mixing device e, a conduit h connecting tank a and evaporator g with pipe c and a conduit f connecting the exit side of a forced draft fan with mixing device e. The arrangement is such that air supplied from the exit side of the forced draft fan and ammonia gas supplied from tank a and evaporator g are mixed in mixing device e and the resultant mixture is injected into flue b through the nozzles or openings j to neutralize the sulfuric acid components, in the waste flue gas, with ammonia. Arrangements of this type are shown, for example, in Hodsman et al U.S. Pat. No. 1,931,408 and Doramus et al U.S. Pat. No. 1,496,410.
The prior art apparatus has had the following disadvantages. Namely, ammonia is injected uniformly into the flue regardless of the distribution of sulfuric acid components in the waste flue gas. Therefore, when a Ljungstrom air preheater is used, with which the temperature distribution and sulfuric acid component distribution tend to become non-uniform at the exit of the heater, under the influence of rotation of the rotor, the amount of ammonia injected locally becomes either excessive or insufficient and, where the amount is insufficient, low melting point compounds are formed (although it has been considered that ammonia sulfate and acid ammonia sulfate are the products of neutralization with ammonia of the sulfuric acid components in a waste flue gas, the composition of the neutralization product is complicated by compounds of extremely low melting points, such as of about 50.degree. C, which may possibly be formed depending upon the molar ratio of NH.sub.3 : H.sub.2 SO.sub.4), which attach to the nozzles to clog the same and promote corrosion rather than preventing it. The apparatus also has had the disadvantage that, since the ammonia-air mixture is injected into the flue at the normal temperature, the nozzle pipes are cooled, promoting the clogging of the nozzles with flue dusts.